The present invention is a medical product that can be used to correct vision loss or even complete blindness caused by certain retinal diseases. A variety of retinal diseases cause vision loss or blindness by destruction of the vascular layers of the eye including the choroid, choriocapillaris, and the outer retinal layers including Bruch""s membrane and retinal pigment epithelium. Loss of these layers is followed by degeneration of the outer portion of the inner retina beginning with the photoreceptor layer. Variable sparing of the remaining inner retina composed of the outer nuclear, outer plexiform, inner nuclear, inner plexiform, ganglion cell and nerve fiber layers, may occur. The sparing of the inner retina allows electrical stimulation of this structure to produce sensations of light.
Prior efforts to produce vision by electrically stimulating various portions of the retina have been reported. One such attempt involved an externally powered photosensitive device with its photoactive surface and electrode surfaces on opposite sides. The device theoretically would stimulate the nerve fiber layer via direct placement upon this layer from the vitreous body side. The success of this device is unlikely due to it having to duplicate the complex frequency modulated neural signals of the nerve fiber layer. Furthermore, the nerve fiber layer runs in a general radial course with many layers of overlapping fibers from different portions of the retina. Selection of appropriate nerve fibers to stimulate to produce formed vision would be extremely difficult, if not impossible.
Another device involved a unit consisting of a supporting base onto which a photosensitive material such as selenium was coated. This device was designed to be inserted through an external scleral incision made at the posterior pole and would rest between the sclera and choroid, or between the choroid and retina. Light would cause a potential to develop on the photosensitive surface producing ions that would then theoretically migrate into the retina causing stimulation. However, because that device had no discrete surface structure to restrict the directional flow of charges, lateral migration and diffusion of charges would occur thereby preventing any acceptable resolution capability. Placement of that device between the sclera and choroid would also result in blockage of discrete ion migration to the photoreceptor and inner retinal layers. That was due to the presence of the choroid, choriocapillaris, Bruch""s membrane and the retinal pigment epithelial layer all of which would block passage of those ions. Placement of the device between the choroid and the retina would still interpose Bruch""s membrane and the retinal pigment epithelial layer in the pathway of discrete ion migration. As that device would be inserted into or through the highly vascular choroid of the posterior pole, subchoroidal, intraretinal and intraorbital hemorrhage would likely result along with disruption of blood flow to the posterior pole. One such device was reportedly constructed and implanted into a patient""s eye resulting in light perception but not formed imagery.
A photovoltaic device artificial retina was also disclosed in U.S. Pat. No. 5,024,223. That device was inserted into the potential space within the retina itself. That space, called the subretinal space, is located between the outer and inner layers of the retina. The device was comprised of a plurality of so-called Surface Electrode Microphotodiodes (xe2x80x9cSEMCPsxe2x80x9d) deposited on a single silicon crystal substrate. SEMCPs transduced light into small electric currents that stimulated overlying and surrounding inner retinal cells. Due to the solid substrate nature of the SEMCPs, blockage of nutrients from the choroid to the inner retina occurred. Even with fenestrations of various geometries, permeation of oxygen and biological substances was not optimal.
Another method for a photovoltaic artificial retina device was reported in U.S. Pat. No. 5,397,350, which is incorporated herein by reference. That device was comprised of a plurality of so-called Independent Surface Electrode Microphotodiodes (ISEMCPs), disposed within a liquid vehicle, also for placement into the subretinal space of the eye. Because of the open spaces between adjacent ISEMCPs, nutrients and oxygen flowed from the outer retina into the inner retinal layers nourishing those layers. In another embodiment of that device, each ISEMCP included an electrical capacitor layer and was called an ISEMCP-C. ISEMCP-Cs produced a limited opposite direction electrical current in darkness compared to in the light, to induce visual sensations more effectively, and to prevent electrolysis damage to the retina due to prolonged monophasic electrical current stimulation.
These previous devices (SEMCPs, ISEMCPs, and ISEMCP-Cs) depended upon light in the visual environment to power them. The ability of these devices to function in continuous low light environments was, therefore, limited. Alignment of ISEMCPs and ISEMCP-Cs in the subretinal space so that they would all face incident light was also difficult.
This invention is, among other things, a system that allows for implantation of microscopic implants into the diseased eye so that the system can function in continuous low light levels, and also produce improved perception of light and dark details. This invention has two basic components: (1) multi-phasic microphotodiode retinal implants (xe2x80x9cMMRIsxe2x80x9d) of microscopic sizes that are implanted into the eye, and (2) an externally worn adaptive imaging retinal stimulation system (xe2x80x9cAIRESxe2x80x9d) that, among other things, uses infrared light to stimulate the MMRIs to produce xe2x80x9cdark currentxe2x80x9d in the retina during low light conditions, and to improve perception of light and dark details.
In its basic form, a MMRI of this invention has, depending upon its orientation, a PiN configuration where the P-side of the implant has light filter layer that permits visible light to pass, and where the N-side of the implant has a light filter that permits only infrared (xe2x80x9cIRxe2x80x9d) light to pass, and preferably only selected wavelength(s) of IR light. In practice, a population of such MMRIs are implanted in the so-called xe2x80x9csubretinal spacexe2x80x9d between the outer and inner retina in the eye such that, randomly, about half of them (i.e. the first subpopulation) will be oriented so that their P sides face light incident to the eye, and about the other half (i.e. the second subpopulation) will be oriented so that their N-sides face light incident to the eye.
In this location and orientation, the first subpopulation of MMRIs convert energy from incoming visible light into small electrical currents to stimulate the sensation of light in the eye to produce formed vision. In other words, the first subpopulation converts visible light to electrical current to stimulate the retina with xe2x80x9clight currentsxe2x80x9d to induce the perception of visible light. The second subpopulation of MMRIs converts infrared light provided by AIRES into electrical currents to stimulate the retina with xe2x80x9cdark currentsxe2x80x9d during low light conditions to induce the perception of darkness.
The adaptive imaging retinal stimulation system or AIRES is comprised of a projection and tracking optical system (xe2x80x9cPTOSxe2x80x9d), a neuro-net computer (xe2x80x9cNNCxe2x80x9d), an imaging CCD camera (xe2x80x9cIMCCDxe2x80x9d), and an input stylus pad (xe2x80x9cISPxe2x80x9d).
In one embodiment of this invention, each microscopic implant comprises plural paired MMRI subunits disposed together in a single flattened cubic unit. The microscopic implants are fabricated so that each MMRI member of each pair has its positive pole electrode on one of the flattened surfaces, and its negative pole electrode on the other flattened surface. Each MMRI member of each pair is disposed so that it is oriented in the opposite direction from the other MMRI member of the pair, the negative (N) electrode of the first MMRI pair member being on or close to the same surface as the positive (P) electrode of the second MMRI pair member, and the positive electrode of the first MMRI pair member being on or close to the same surface as the negative electrode of the second MMRI pair member. Each of the flattened sides of a single microscopic implant therefore, has at least one associated positive microphotodiode electrode from one MMRI and one negative microphotodiode electrode from another MMRI. This symmetry ensures that each such microscopic implant functions in exactly the same manner regardless of which of the flattened surfaces faces incident light. Multiple layer dielectric filters are disposed on the P surfaces and N surfaces of the MMRI subunits to allow visible light (400 to 740 nm) to pass through to the P surfaces and infrared light (740-900 nm) to pass through to the N surfaces. In this manner, the PiN configuration of each MMRI subunit responds to visible light while the NiP configuration responds to infrared light.
In a modification of this embodiment, a common electrode, on each side of the implant, connects the positive pole electrode of one MMRI member to the negative pole electrode of the second MMRI member on the same side.
In the preferred embodiment, the flattened microscopic implant structures typically have a thickness to width and depth ratio of 1:3 and have a preference to orient themselves, within the subretinal space, with one of their flattened photoactive surfaces positioned to accept incident light. The P and N electrodes of each MMRI subunit, and/or the common electrode connecting the P and N electrodes, are on or close to the microscopic implant""s light sensitive surfaces. Electric currents produced by the PiN configuration will stimulate the sensation of xe2x80x9clightxe2x80x9d in the overlying and/or adjacent retinal cells, while electric currents produced by the NiP configuration will stimulate the sensation of xe2x80x9cdarknessxe2x80x9d in the vicinity of those same cells.
The power for the xe2x80x9clight currentsxe2x80x9d is derived from the visible spectrum of light from incoming images. The power for the xe2x80x9cdark currentsxe2x80x9d is provided by superimposed infrared (JR) light and/or images projected into the eye by an external computer-controlled optical headset system. This external computer controlled headset projection system is the second component of the artificial retinal device of this invention and is called the Adaptive Imaging Retinal Stimulation System xe2x80x9cAIRESxe2x80x9d.
AIRES is comprised of component sub-systems of: a Projection and Tracking Optical System (PTOS), a Neuro-Net Computer (NNC), an Imaging CCD Camera (IMCCD), and an Input Stylus Pad (ISP). During operation, AIRES xe2x80x9cseesxe2x80x9d and interprets details and characteristics of images via its own IMCCD and processes this information with its NNC. It then projects modulated infrared light and/or images, and visible light images if necessary into the eye to modify implant function. By the use of a partially reflective and transmissive mirror in the PTOS, AIRES projects IR and visible light/images that are superimposed over the visible spectrum images passing into the eye from the environment. Initially, AIRES will be programmed using xe2x80x9cpatient inputxe2x80x9d from an input device, such as a stylus pad, to xe2x80x9ctrainxe2x80x9d the NNC on how to modify implant function to produce accurate images. After training, AIRES will have an improved capability to modulate implant function with little additional patient assistance. The primary advantages of this MMRI plus AIRES combination system over the previous art is that the combined system can still function in low light environments and that xe2x80x9clightxe2x80x9d and xe2x80x9cdarkxe2x80x9d currents may be finely tuned by AIRES to provide optimal images. The production of opposing light and dark currents will also decrease any damaging effects from electrolysis, and improve implant biocompatibility.
In the preferred embodiment, the AIRES PTOS headset is worn by the patient, and projects variable intensity IR and visible-light images and illumination into the eye, by using an IR and visible-light capable CRT (IRVCRT). These IR and visible-light images and illumination will modify the function of the M subunits of the implant by modulating their current output. In darkness, IR illumination is the predominate power source and powers the MMRI NiP configuration to produce electric currents that will stimulating the visual sensation of darkness. However, the IR induced NiP current is modified by the PTOS through NNC control, based upon information provide by the PTOS""s ambient light sensors and IMCCD. Under bright lighting conditions, a higher current will be induced in the MMRI PiN configuration by ambient light, and will offset a modulated lower MMRI NiP current. This produces a net perception of light. Because images in the normal environment have constantly changing light and dark qualities, the implants will also rapidly change their electrical outputs between xe2x80x9clight currentsxe2x80x9d and xe2x80x9cdark currentsxe2x80x9d. Modulation of the implant xe2x80x9clight currentxe2x80x9d can also be performed by the AIRES PTOS by projecting additional visible light images, superimposed over the ambient light images.
During operation, AIRES uses its NNC to process digitized images provided by its IMCCD. In the preferred embodiment, AIRES projects superimposed, real-time-video, visible and infrared images onto the retinal implants. These images may be displayed either simultaneously or in rapid succession from the IRVCRT. Alternatively, any appropriate display device such as a filtered active matrix LCD, LED display, or filtered plasma display may be used to produce the visible and IR light and images. AIRES controls the PTOS projected images by changing their wavelengths, intensity, duration, and pulse frequency. A patient input device (e.g. an Input Stylus Pad) is also interfaced with the NNC and allows the patient to modify the IR and visible light images produced by the PTOS headset. This patient xe2x80x9cfeedbackxe2x80x9d is analyzed by the AIRES NNC, then compared with the computer processed images from the IMCCD, and the differences learned by the AIRES Neuro-Net software. After a teaching period, the NNC is able to automatically adjust the computer generated visible and IR images to improve image quality without assistance by the patient. By adjusting the stimulating frequency and duration of the PTOS IR and visible images, AIRES will also be able to stimulate the sensation of color in some patients. This is in a manner similar to color sensations induced in normal sighted persons, by using a spinning black and white Benham top, or by using frequency modulated black and white television monitors.
The MMRI and AIRES components of this invention differ from the previous art primarily in the following ways. Visible and infrared images and light are used to selectively modulate MMRI function. A MMRI can be stimulated with light from either of its two photoactive sides and produce localized stimulating electric current from both sides. The flattened shapes of the MMRIs allow preferential orientation of the devices toward incident light when disposed in the subretinal space. Using the AIRES system, electrical output from MMRIs can be programmed for individual patient needs. The design of the MMRIs also allows the alternative to use them to stimulate the nerve fiber layer, ganglion cell layer, or inner plexiform layer of retina from vitreous body side; or to use them to stimulate the remnant photoreceptor layer, bipolar cell layer, or the inner plexiform layer from the subretinal space, by reversing their polarities during fabrication. The biphasic nature of the electrical current output from MMRIs are also better tolerated biologically than the mostly monophasic nature of electrical stimulation of the previous art.